点源文件中的PowerShell点源 - 导入类

Question

My project is structured like this:

MyScript.ps1
classes\
    Car.ps1
    Tesla.ps1

Car.ps1 is the base class of Tesla.ps1. I attempt to define Tesla like this in Tesla.ps1:

. "$PSScriptRoot\Car.ps1"

class Tesla : Car
{
}

MyScript.ps1 needs to use the Tesla class, but shouldn't need to know that it inherits from Car.

. "$PSScriptRoot\classes\Tesla.ps1"

$tesla = [Tesla]::new()

Dot sourcing to classes\\Tesla.ps1 works fine, but this error is thrown from the Tesla file:

Unable to find type [Car]

If I import all the files in the correct order in MyScript.ps1, it works fine. Example:

. "$PSScriptRoot\classes\Car.ps1"
. "$PSScriptRoot\classes\Tesla.ps1"

$tesla = [Tesla]::new()

This is cumbersome, especially as the complexity grows. Am I dot sourcing incorrectly? Is there a better way to import a custom PowerShell class using a relative path that isn't in the PSModulePath?

Answer 1

PetSerAl , as countless times before, has provided the crucial pointers in a terse comment on the question:

Due to your use of classes , you must use modules and import them with using module statements in order to use them.

^{Unfortunately, as of this writing, using module is still not mentioned in Get-Help about_Modules ).}

Specifically, in order to reference a type (class) in a class definition, that type must be known to PowerShell at parse time .

In your example, in order to derive Tesla from class Car , type Car must be known to PowerShell when the script is parsed , before execution begins - that's why it is too late to try to import Car by dot-sourcing its containing script ( . "$PSScriptRoot\\Car.ps1" )

PowerShell knows about referenced types at parse time in one of two ways:

• If the type is already loaded into the current PowerShell session

• Via a using module statement that references a module in which the type (class) is defined (note that there's also a using assembly statement for loading types from DLLs, and using namespace to enable referring to types by their mere names).

  • Note that the related Import-Module cmdlet does not work in this case, because it executes at runtime .

Therefore, as PetSerAl suggests:

• Store your classes in module files (stand-alone *.psm1 files in the simplest case)

• Then use using module to have the Tesla module import the Car module and the MyScript.ps1 script import the Tesla module, using paths that are relative to the enclosing script / module's location .

  • Caveat : As of PowerShell Core 6.1.0-preview.4, there is a bug that requires that you use \\ as the path separator in relative paths with using module , even on Unix-like platforms, where you'd normally use / .

MyScript.ps1
classes\
    Car.psm1    # Note the .psm1 extension
    Tesla.psm1  # Ditto

Car.psm1 :

class Car {}

Tesla.psm1 :

using module .\Car.psm1

class Tesla : Car {}

MyScript.ps1 :

using module .\classes\Tesla.psm1

$tesla = [Tesla]::new()